Abrasive supporting pad



y 1939- R. c. BENNER ET AL 2,157,037

ABRAS IVE SUPPORTING PAD Filed Dec. 30, 1955 g I AM INVENTORS. RAYMOND QBENNER CHARLES E WOODDELL' CHARLES SIN EL$ON ATTORNEY.

Patented July 25, 1939 .UNlTEiD STATES PATENT OFFICE ABRASIVE SUPPORTING PAD tion of Delaware Application December 30, 1935, Serial No. 56,707

2 Claims.

The present invention relates to surfacing apparatus and is particularly directed to an improved supporting pad for use insurfacing apparatus of the type now commonly employed for grinding, polishing and similarly treating surfaces such as' panels of wood, metal and other materials and such articles as castings, automobile bodies, fenders and the like.

Apparatus capable of such operation usually includes a flexible power driven shaft provided at one end with appropriate encased gearing and handles for an operator. A supporting pad, against which has been removably secured an abrasive element, is mounted on the end of the flexible shaft and rotated thereby. The flexible shaft permits the supporting pad carrying the abrasiveelement to be manually moved over the surface of the material to be ground or polished.

The present invention is directed to a new and improved pad for use in connection with apparatus of the above character.

The pads that have been used in the past as a backing for an-abrasive element have been usually formed of wool felt. A felt pad has been found in actual operation to be sufilciently yieldable to flex and thus permit the abrasive element to follow the surface of the material being ground or polished. In connection with the operation of felt pads, it has been found they will not absorb punishment such as excessive flexing and the fibers of the felt often separate at a point adjacent a metal reinforcing plate that is used in the back of such pads. The continual flexing and subsequent distortion of the fibers of the felt and the internal friction of the felt has been' known to cause the temperature of the pad to be raised above the ignition point of felt and the resulting burning marks the end of the useful life of such pads.

Pads formed of laminated fabric and rubber have been tried for this type of abrasive backing but the result found unsatisfactory due to the separation of the rubber and fabric as a result of internal friction which raises the temperature under the operating stresses.

Another type of pad used in the past has been one constructed of vegetable fiber. In the construction of such a pad the fiber is arranged in a longitudinal continuous group and as such wound in a spiral juxtaposed fashion to form a relatively thin circular disk. The use of such a pad in actual operation has not been entirely satisfactory. The juxtaposed spiral convolutions have very little lateral cleavagewith respect to, each other and outer spirals or convolutions of; fiber tend to break away from their inner or lower convolutions, as a result of flexing near the outer periphery of the pad. Pads formed of spiraled vegetable fiber have therefore a comparatively short useful life which renders them undesirable as a sander or abrasive supporting pad. Another disadvantageous feature of such pads results from the fact that they can only be operated in one direction of rotation since operation in a. direction opposite to that by which the fiber is wound will tend to loosen or unwind the spiraled convolutions.

Another disadvantage of such pads results from the longitudinal parallel arrangement of fiber and the close association thereof prevents the impregnating compound from reaching and coating all of the individual fibers, and a proper bond between the fibers is therefore absent in a supporting pad formed with such a fiber arrangement. The fibers are not held apart by the binding material since the compound does not reach and coat every fiber. The fibers and particularly the centrally located strands of the group therefore frictionally engage each other during lateral distortion of the pad. It is apparent that under such conditions the fibers will soon be ruptured in operation if the pad has not already disintegrated as a result of the spiralled fibers leaving small cleavage of the lower convolutions when the lateral pressure is applied to the pad.

An object of the present invention is therefore to provide an abrasive supporting pad with the desired qualities of flexibility which will at the same time resist destruction as a result of the internal stresses set up by distortion of the pad.

Another object of the invention is the provision of a simple and inexpensive pad of the character described and one which may be easily manufactured and with various structural differences and therefore of various. qualities of flexibility to meet the demand of the trade in the various surfacing operations.

In the accompanying drawing:

Figure 1 is a central sectional view of one type of supporting pad also showing a mounting hub in section.

Figure 2 is a transverse central section showing a modification of'the pad of Figure 1.

Figure 3 is a view in side elevation showing the pattern, to form what may be termed a fibrous felt. The numerous relatively long fibers composing the felt are intermingled and interlocked with each other, and one individual fiber may cross and recross another or many other individual fibers. Such an arrangement of fibers in the nature of felt, forms .a convenient method of handling the fiber in the construction of 'an abrasive supporting pad. The term "felted fiber" as used herein pertains to such an arrangement of fiber as above described.

In practicing the invention the use of felted fiber is contemplated, and, in a preferred form of our invention, felted fiber of the hemp family such as sisal, manila or jute may be used in forming the body of the supporting pad. It is to be understood, however, that other intermingled non-parallel arrangements of fiber may be employed.

The felted fiber in the initial state is a rel-' atively loose mass of fibers and the fiber may be felted in sheet form of varying thickness'from a fraction of an inch to a sheet of several inches. The fibrous felt sheet in its initial state is impregnated with a fluid bonding compound which may be applied in any well known manner. The loose arrangement of the individual fibers of the felt provides an important advantage to the present method of fabricat ng an abrasive supporting pad, since the individual fibers may be easily coated by an impregnating compound. Care must be exercised in applying the compound to the feltso that every fiber will be provided with a coating of the compound. It may be necessary in some cases to repeat the impregnating operation so that every fiber will be properly coated. Any compound which may be congealed or vulcanired into a yieldable bond may be used to saturate the felt. In a preferred embodiment of our invention, a liquid vulcanizable compound such as the following is used:

- Per cent. Pale crepe rubber 94.26 Sulphur 0.65 Tuads 1.12 Telloy 0.22 ZnO 1.78 Stearic acid 0.89 Anti-oxidant 0.48

12% solution in rubber gasoline.

The felted sheet is then 'dried or permitted to dry and cut or shaped into the form of a circular disk. An abrasive supporting pad may be formed from a single relatively thick felted fiber disk. However, it may be desirable to arrange sive supporting pad. The heat application of the mold vulcanizes the compound with which the fibers have been previously impregnated, binding the individual fibers to each other and forming in an, integrally united manner there-- with a thin coating of vulcanized rubber along the entire surface of the felted fiber disk. The

heat application also vulcanizes the rubber along the surface of the individual fibers and binds the intermingled fibers to each other in a spaced contact relation so that a substantially unitary structure of consolidated fiber is formed by the compression and application of heat.. The film cl-rubber formed over the surfaceof the fibers are-2,037

prevents frictional contact of the adjacent fibers when the pad is operated in a distorted fashion.-

-As above indicated, in a preferred embodiment of the invention, a vulcanizable compound is used as a binding agent. It'will be apparent however, that bonding compounds may be used to unite the fibers into a yieldable structure such as the flexible alkyd resins. A yieldable bond of this type may be formed by heating one mol of glycerol and 1.5 mol of sebacic acid at 170 C. to form a semi-fluid compound which becomes a firm plastic resin when cured and permitted to return to a normal temperature. A resin of this type does not become brittle on exposure to light and maintains strength and resiliency after a long period of use. When a bonding agent of the latter type is used, the felted fiber is impregnated with a solution of the synthetic resin to properly coat the surface of all of the individual fibers. The

felted fiber is then formed into a substantial pad shape and compressed in a mold to consolidate the felted fiber disks into the shape of a. finished pad,.and the compressed mass is cured in a consolidated condition-to form a finished abrasive supporting pad.

Another type of resin such as Aivar may be employed to bind the fibers in a yieldable mass. Such a resin is known as a polyvinyl acetal type and is obtained by replacing part or substantially all of the acetate groups in vinyl acetate resin by acetaldehyde. A resin of this, nature is relatively fiex-lble and may be made more so by adding a plasticizer such as butyl-pthalate.

Referring to the drawing, there is shown in Figure 3 a surfacing apparatus consisting of a frame or casing ll provided with angularly related handles l2 and i3 of which the handle I! is hollow and adapted to receive a driven flexible shaft (not shown). The frame or casing II is adapted to house and internallysupport a suitable connecting gear (not shown) so that the shaft ll extending from the lower side of the casing will be rotated by the driven flexible shaft. The shaft I4 is adapted to removably receive the improved supporting pad.

The supporting pad, as shown in Figure 1, consists of a circular disk body portion It. The body porton I6 is formed of felted fiber, which has been impregnated with a vulcanizable compound cut and compressed into a circular disklike pad by means of a heated mold. The two substantially fiat faces" and I! of the felted fiber disk, the peripheral edge 19 and the inner edge II are provided with a relatively thin coating ofvulcanized rubber which is formed and integrally united with the felted fiber when the same is compressed in a heated mold.

The pad may be mounted on the shaft It by means of a hub member 23 internally threaded to be removably received over the threaded lower end 24 of the shaft ll. The pad proper is secured to the hub member 23 by means of a supplementary hub H which is adaptedto engage the under surface of the pad adjacent a central opening 26. A plurality of bolts 21 extend through a reinforcing portion 20 of the hub 28' at circumferentially spaced intervals and pass through a plurality of similarly spaced openings II in the supplementary hub 24 and engage a plurality of nuts 32 carried by the supplementary hub, and

the pad is thus removably secured to the hub:

member 23.

It is desirable in various surfacing operations to support the abrasive with pads of various ficting qualities, and this is accomplished by con- 7} structing the pads of various degrees of thickness and combinations of felted'fiber. In carrylng out these requirements, pads of different resistance to distortion or fiexing may be formed by varying the amount of impregnating compound, and the manner in which the compound is applied to the felted fiber or by varying the initial thickness of felted fiber, or the pressure under which the fiber is compressed. The resiliency may in other words he modified by the amount of fiber per unit of volume and/or the amount of bonding material per unit of volume. The modification shown in Figure 2, for instance, is formed from two disks of felted fiber 34 and 36. In this modification the felted disks are impregnated with a vulcanizable compound and an additional amount of the compound is applied between the fiat surfaces of the fiber disks 34 and 36 so that the compressing mold and application of heat vulcanizes a layer of rubber 31 between the disks which is integrally united with the two layers of the compressed felted .fiber 34 and 36. The layer of rubber 31 in addition to binding the fibers of the two disks also acts as a reinforcing member and tends to prevent abnormal lateral distortion of the pad when placedfin operation on a work surface. It will be appreciated that by varying the amount of the impregnating compound, the number of layers of felted fiber and the amount and application of the impregnating compounds, pads'may be constructed which will differ in their ability to resist distortion.

In the formation of the present pad a felted fiber has been utilized for the purpose of increasing the useful life of the pad by providing a pad which will resist destruction when operating in a distorted fashion as a result of the attendant internal friction, caused by stresses which have been set up by lateral pressure on the pad and flexing thereof near the periphery.

The arrangement of the fibers of the felt in the present invention is distinctly different from an arrangement of continuous fibers in parallelism with one another and longitudinally of their continuous lengths. If the fibers are arranged in a longitudinal parallel relation and. then spiralled with a series of superimposed convolu-- tions into a disk-like pad, it will be appreciated that very little cleavage will be provided between the parallel fibers and such a pad will resist but a small lateral force before the longitudinal fibers part and the pad is destroyed.

The present pad has been devised to overcome the disadvantages of such an arrangement of fiber in abrasive supporting pads. In our pad consisting of felted fiber the strands or fibers are crossed, intermingled, and interlocked with other fibers to such an extent that reinforcement is provided against lateral distortion. Pads, constructed in. accordance with thepresent invention and as above described, may be flexed under lateral pressure in actual surfacing operations and will not readily disintegrate as a result of the internal stresses which necessarily result from the operation of surfacing apparatus of this character. 3

It will also be apparent that the felted fiber permits the individual fibers to be impregnated in such a manner that a surface coating of every fiber is possible. The compound covering the individual fibers binds the fibers to each other in spaced relation so that frictional contact between the fibers is impossible. The present abrasive supporting pad will therefore absorb considerable punshment in actual operation under distortion as a result of lateral pressure since the internal friction has been reduced to a negligible value and the reinforcement is provided to maintain the constant resiliency of the pad.

We claim:

1. A supporting pad of the character described comprising a plurality of felted fiber disks, a disk of vulcanized rubber, one of said fiber disks being arranged adjacent each face of said rubber disk,

compressed into a disk-like body and a coating of rubber covering the entire surface of said body.

2. The method of making an abrasive supporting pad which comprises impregnating felted fiber with a binding compound to coat every fiber thereof, shaping the felt into the form 'ofa circular .disk, applying a surface coating of the compound to each face of the disk and thereafter curing said compound while the felt is compressed to bond the fibers of the felt in a consolidated state and to provide a layer of the 

